1. Field of the Invention
This invention relates to a control system for a gas turbine aeroengine.
2. Description of the Related Art
In a control system for an aircraft engine, the data on the engine inlet conditions including Mach number, pressure altitude and outside air temperature are generally detected from outputs of engine inlet sensors such as a temperature sensor and a pressure sensor, all installed at the inlet (air intake) of the engine. When an aircraft has an on-board computer installed in the airframe, the airframe on-board computer determines the engine inlet condition data and sends the same to a computer of an engine control system installed at the engine. Even if the engine computer is merely provided with the data from the airframe computer, the engine computer still needs the inlet sensors as a backup for a case when the engine computer is not able to receive the data from the airframe computer due to, for example, a communication trouble therebetween.
For that reason, an ordinary prior art control system is provided with a temperature sensor and a pressure sensor installed near an air intake (engine inlet) at the front of an engine (turbofan engine) for detecting the intake air temperature (herinafter referred to as xe2x80x9cT1xe2x80x9d) and the intake air pressure (hereinafter referred to as xe2x80x9cP1xe2x80x9d) at that location.
Since, however, these engine inlet sensors such as the temperature sensor and the pressure sensor are located near the intake (engine inlet), the sensors are liable to suffer from the problem of FOD (Foreign Object Damage) and/or icing. Therefore, the engine inlet sensors require a sufficient strength to prevent them from being damaged by foreign objects such as birds and hail. Moreover, the sensors need a temperature raising means such as a heater to avoid being iced over. Accordingly, the engine inlet sensors are generally expensive.
Therefore, it is preferable to remove the engine inlet sensors and to estimate the engine inlet condition data based on outputs from the other sensors.
As regards the parameter estimation, U.S. Pat. No. 4,249,238 proposes a gas turbine engine control system which maintains a selected level of engine performance despite the failure or abnormal operation of one or more engine parameter sensors.
However, this prior art does not disclose removing any sensor such that the necessary data is estimated from an output(s) of other remaining sensors. Moreover, the parameter estimation proposed by this prior art requires an engine model which should be updated on a real-time basis. This disadvantageously makes the configuration of the system complicated.
An object of this invention is therefore to overcome the problems of the prior art by providing a control system for a gas turbine aeroengine that, without using the engine inlet sensors and instead, enables it to estimate necessary engine inlet condition data based on outputs from other sensors through reasoning or logic with a relatively simple configuration.
For realizing this object, the present invention provides a system for controlling a gas turbine aeroengine having at least a turbine which is rotated by gas produced by the engine to rotate a rotor that sucks in air, comprising: turbine rotational speed detecting means for detecting a rotational speed of the turbine; turbine inlet pressure detecting means for detecting an inlet pressure of the turbine; atmospheric pressure detecting means for detecting an atmospheric pressure exerting on the engine; and engine inlet condition data estimating means for estimating engine inlet condition data based at least on the detected rotational speed of the turbine, the detected inlet pressure of the turbine and the detected atmospheric pressure.